Top Docker Interview Questions You Must Know In 2022-23

By Archer Charles 22-Dec-2022
Top Docker Interview Questions You Must Know In 2022-23

Docker became a part of the IT industry in 2013. Since then, it has grown without looking back, with its container image download numbers reaching over 8 billion by 2017. The rising demand for Docker also resulted in significant growth in jobs and demand for trained Docker professionals.

Going prepared for an interview will never disappoint. Not only should you have your references and resume memorized like the back of your hand, but you also need a solid understanding of everything the position requires and a little about the company. Showing an interviewer that you have researched the company proves that you are genuinely interested in it and have put in the time and effort to study them.

You also need to have enough knowledge about the subject matter. While there’s no way to predetermine all the Docker interview questions you will face, you can still prepare well enough to have a proper conversation. The best way to do this is to research the most common interview questions and understand how to answer them. Once you do that, you will be able to take on related questions. It will also give you more confidence in your interview.

To understand all the relevant Docker Basic Questions and get expert guidance before your interview, you can also enrol in a Docker training course on Koenig. Get a more holistic approach when you enrol in a training course today.

25 Popular Docker Interview Questions You Should Prepare For

Q1. Define Docker!

Docker is one of the world’s leading containerization technologies. It is a lightweight open-source solution popular in the app packaging and cloud domains. Docker helps businesses automate app deployment by dividing it into portable and lightweight containers.

Q2. What are the greatest advantages of Docker Containers?

There are several benefits of Docker for enterprises. These include:

- A simple and efficient initial infrastructure set-up

- Enables businesses to describe in detail their app lifecycle

- Simple configuration

- Docker Compose interaction functionality

- Shares all necessary information through its documentation

Q3. What are Docker’s Most Critical Features?

The fundamental features of Docker are:

- Version control

- Easy modelling

- Application agility

- Placement or affinity

- Operational efficiencies

- Developer productivity

Q4. What do you know about Docker Image?

Docker image helps in creating Docker containers. Users can create a Docker image using the ‘Build’ command. This will make a container which starts as soon as it runs. The Docker registry stores every Docker image made.

Q5. What do you know about Docker Engine?

Docker engine or daemon represents the Docker server. Clients and the daemon must always run on a remote host or the same host that communicates through a full REST API and client’s command-line binary.

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Q6. What is a Docker Registry?

Docker registries can be categorised into two types:

- Private Registry

- Public Registry

The public Docker registry is known as Docker Hub and enables businesses to store Docker images privately. Docker Hub can generally store images well into the millions.

Q7. What is the command for viewing all the running containers in Docker?

This command is -> $ docker ps

Q8. What is the command that stops a container that is running?

This command is -> $ sudo docker stop container name

Q9. Which command helps a Docker image run as a container?

This command is -> $ sudo docker -i -t alpine/bin/bash

Q10. What are the most common instructions given in Dockerfile?

FROM, RUN, CMD and LABEL are the Dockerfile common instructions.

Must Read: Top DevOps Interview Questions and Answers

Q11. What is a memory-swap flag?

This refers to a modified flag with meaning only under the condition that the memory is set too. Swap helps the container write memory needs to a disk when containers exhaust all the available RAM in the local system.

Q12. Explain Docker Swarm very briefly.

Docker Swarm is a native Docker gathering designed to help businesses connect to several Docker Hosts into one virtual host. Docker Swarm provides businesses with the standard Docker app interface.

Q13. How can you monitor Docker in a production environment?

Businesses use Docker events and Docker states to monitor Docker within production environments.

Q14. What are the different states a Docker container goes through?

A Docker container’s important states are running, restarting, pausing and exiting.

Q15. What is Docker Hub?

As mentioned before, Docker Hub refers to a public Docker registry based on the cloud that helps enterprises connect with code repositories. Hub enables businesses to build, store and test Docker images in the cloud. Additionally, they can deploy images to their hosts using Docker Hub.

Q16. What is virtualization? Explain!

Virtualization is a technique of dividing mainframes logically, allowing several apps to run at the same time. However, virtualization has seen a change ever since businesses as well as open-source communities started providing a method to handle privileged instructions. This allows several operating systems to run on singular x86 systems simultaneously.

Q17. What can you tell me about Hypervisor?

Hypervisors enable users to create virtual environments in which guest VMs can operate. A hypervisor controls guest systems while ensuring guests get allocated all the necessary resources.

Q18. What are Docker Object Labels?

Think of Docker Object Labels as a process used to apply metadata to images, volumes, containers, services, swam nodes, networks and other Docker objects.

Q19. Give an example of a Docker file used for creating and copying a directory. Build it with Python modules.

An example of this situation is

FROM python:2.7-slim


COPY ./app

docker build -tag

Q20. Will cloud overtake containerization in the coming years?

Docker containers have become increasingly popular today but are almost paralleled by cloud services in terms of growth. However, there’s enough reason to believe that cloud services cannot replace Docker. Instead, combining cloud services using containerization will take the capabilities of both technologies to a whole new level. In situations where either of the two technologies can be used, businesses must choose after looking at their specific requirements instead of following existing trends. Most organisations today use Docker with cloud integration. This gives them the best of both technologies and enables improved service offerings and business growth.

Q21. How many containers per host can be run?

A single host can run as many containers as they wish or require. Docker has not placed any restrictions on the number of containers. However, every container requires storage space, which is represented by the CPU and other memory hardware required for support. Businesses should also consider the size of the application. Docker containers are usually lightweight, but that depends heavily on the hosting operating system.

Q22. Is it generally considered a good practice to use Docker to run stateful apps?

Stateful applications are built on the concept of storing data on their local file systems. If users move the app to a different machine, data retrieval is a cumbersome process. Therefore, experts recommend that Docker should not be used to run stateful applications regularly.

Q23. Consider a situation where you have an app with several dependent services. Does Docker Compose wait for your present container before it is ready to move ahead and run the next service? Explain.

The short answer is yes. Docker Compose will always run in the order of dependency. Each dependency is a specification such as links, depends_on and volumes_from.

Q24. Which changes should you make in a personal Docker Compose file before it moves to production?

Some changes are essential in a Docker Compose file before migrating the application to a production environment. These are:

- Removing volume bindings to ensure the code remains within the container will mean no one can change it from outside.

- Binding to separate localhost ports

- Adding log aggregator and other extra services

- Specifying a restart policy

Must Read: Top VMware Interview Questions and Answers

Q25. What do you know about load balancing done across hosts and containers? Can you explain how it works?

When you use Docker with several containers across multiple hosts, you find that load balancing all incoming traffic is a necessity. HAProxy and load balancing are generally used to balance this traffic across various healthy or available containers. If any container crashes for any reason, a separate container should start running automatically, and the traffic must get rerouted to it. Both HAProxy and Load Balancing operate on this concept.

And there you go. While these Docker interview questions and answers are not necessarily asked exclusively in every interview, several of these questions do appear in most interviews in some form or other. While preparing for these, you will get the confidence and peripheral knowledge to understand other related concepts of Docker as well. This all adds up to higher chances of clearing your Docker job interview on the first attempt.

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Archer Charles

Archer Charles has top education industry knowledge with 4 years of experience. Being a passionate blogger also does blogging on the technology niche.